A prior art complex magnetic head of this type shown in FIG. 3 comprises a center core 11, a channel-shaped recording and reproducing core 12 and a channel-shaped erasing core 13 in which latter two members are disposed at opposite sides of the center core 11 so as to sandwich the center core 11, and they all are united together by glass or other adhesive material 14. The center core 11, recording and reproducing core 12 and erasing core 13 are made from a magnetic material respectively. A space between opposed surfaces of the center core 11 and the recording and reproducing core 12 is selectively padded with glass or other non-magnetic material to define a recording and reproducing gap 16. Similarly, a space between opposed surfaces of the center core 11 and the erasing core 13 is selectively padded with glass or other non-magnetic material to define an erasing gap 15. The magnetic core assembly is inserted in a slot 18 formed in a slider 17 shown in FIG. 5 and is fixed there by glass or synthetic resin. Coils (not shown) are wound on to the recording and reproducing core 12 and the erasing core 13, passing through coil holes 12a and 13a, respectively. One surface 19 of the slider 17 opposed to a magnetic recording medium is wrapped. Thus a complex floating type magnetic head is formed.
Magnetic recording mediums for which the complex, floating-type magnetic head is used have gradually been reduced in size from 3.5 inches through 3.0 inches to 2.5 inches. As shown in an enlarged view of FIG. 6, as the diameter of a magnetic recording medium 20 decreases, a difference is produced in a radially inward portion between an erased area A by the erasing gap 15 and a recorded area B by the recording and reproducing gap 16. The difference causes an excessive erasure or insufficient erasure on the magnetic recording medium, and invites a significant problem about the reliability of the magnetic head. In some cases, the difference will be eliminated by simply decreasing a gap distance L (FIG. 3) between the erasing gap 15 and the recording and reproducing gap 16. However, since the prior art complex magnetic head uses a magnetic material as the center core 11, a decrease in the gap distance L causes a so-called cross-feed phenomenum. That is, a magnetic field generated at the erasing gap 13 leaks to the recording and reproducing core 12 through the magnetic center core 11. Therefore, no significant decrease of the gap distance is expected in the prior art magnetic head.